The disclosed invention is directed generally to an optical alignment system, and more particularly to an optical alignment system for optically aligning the tape head assembly of a computer tape cartridge drive by non-contactive optical gauging.
Computer data tape drives have been utilized for many years in the computer environment for "secondary" storage by which computer data on "primary" storage such as magnetic disk systems could be periodically backed up or transported.
The tape media for the tape cartridge drives is packaged in relatively small tape cartridges, and the write and read heads for a tape cartridge drive are typically contained in a unitary tape head assembly. For accurate recording and reading, it is important that the tape head gaps for a given track be parallel to the tape movement direction and, in accordance with industry standards, a tape cartridge includes reference surfaces that engage fixed position locators in a tape drive intended to receive the cartridge. The fixed position locators define reference planes, and the write and read head gaps must be aligned with a particular reference plane for proper operation.
Tape head assembly alignment has been previously achieved with an alignment system that includes a video microscope mounted on a computer controlled XYZ translation assembly and a reference plate that is configured to position a drive being aligned so that a reference or datum plane defined by certain fixed position locators in the drive is orthogonal to one of the translation axes, for example the Z axis.
The reference plate can be configured to resemble a tape cartridge, for example, and the alignment system is calibrated with a calibration block that represents an ideally aligned tape drive. Calibration is achieved by moving the microscope objective lens so as to superimpose a reticle over each of the scribed cross-hairs on the calibration block which represent ideal tape head gaps that are at the same distance from the reference plane defined by the fixed reference locators, which would be along the Z axis for the example of a reference plane that is orthogonal to the Z axis. The positions of the translation stages at which the reticle is superimposed over the scribed cross-hairs are stored, and the XYZ offsets between the two locations are determined and stored for later use. For alignment, a tape drive is locked onto the reference plate, and the microscope objective lens is moved between two viewing positions for respectively viewing two head gaps whose positions are intended to correspond to the ideal head gap positions represented by the calibration block. The tape head assembly is adjusted so that both gaps are at the same distance from the reference plane, which may involve iterative adjustment and movement of the microscope lens between the two head gaps.
A consideration with the foregoing alignment system is the physical attachment of the reference plate to the alignment system, which may make it incapable of being used with self-loading tape drives wherein the tape cartridge is moved in a plurality of directions for loading. A further consideration with the foregoing alignment system is the necessity of frequent calibration, and the requirement of precise parallelism between the reference plane as defined by the reference plate and one of the translation planes of the translation assembly.